U.S. Pat. No. 3,740,045, "Precision Disc Springs" by J. C. Westmoreland, describes a disc spring arrangement in which a pair of annular disc spring elements are arranged parallel to one another with their outer edges maintained at a first spaced arrangement and their inner edges at a second and greater distance. A plurality of ball bearings contactingly engage the inner edges of the annular spring elements, and a shaft extends through the central opening of the spring elements having a circumferential cam which on moving past the ball bearings, engages the ball bearings and forces them into the space between the spring elements. This action produces a reactive force which, when the cam passes the point of maximum ball bearing extension, drives the shaft further in the same direction at a rate and with a pulselike force depending upon the spring characteristics. Return of the shaft back along the same path causes a similar action in the reverse direction.
Although the patented device is excellent for providing a pulsed shaft actuation, there are many circumstances in which it is desirable to be able to provide a controlled and predetermined rate or plurality of different movement and force actuation rates.